Over flow question

[daplatapus]

OK, maybe this is going to sound a bit weird but I'm having a bit of a hard time wrapping my head around something. If you have a Herbie overflow, and you've got it dialed in just right (by the way what a PITA with ball valves), you're main drain is taking all the pump can give it and your safety drain is an extra 1/4" to 1/2" higher than the water level in your overflow.... everything is running smooth...
Now down in your sump, you've got an ATO that pumps in fresh RO/DI water into your return chamber as water evaps... but what if, in fact, the water isn't evaporating, and your main drain is slowing for some reason, algae, a snail, whatever? As the water level increases, your safety drain kicks in, but to do that your main system rose at least a couple gallons which would have kicked in your ATO, wouldn't it. And now your system really has several gallons of water that isn't really in the design...
Or am I reading too much into this... (or perhaps I've designed my system with not enough room for error)

[evsalty]

I run the backup drain just slightly in the water so that a tiny bit is trickling thru it. Any fluctuations from my wavebox are quickly taken up and drained down to the sump in the emergency drain. Now if something clogs the main drain then yes the DT overflow level rises a tad and the ATO tops off when truely not needed. If I see this or other level issues (had a nylon washer get into my pump earlier this week) I look for the cause of the problem and remedy it. Then the system goes back to normal. So far in almost a year of using it I have not had any other issues with mine.